I Saw Him First
by Watermelonsmellinfellon
Summary: Sherlock is a mutated merman who is looked down upon for his appearance. He lives far away from the pod and prefers to stay in his chosen cove. And then one day, an amazing creature makes its way into his home and Sherlock is shocked to learn of other creatures besides the humans and his fellow merfolk. He also becomes possessive of this creature and wants to keep him for himself.
1. Chapter 1

**A/N: Hello, people! My first Merlock fic!**

 **I don't own Sherlock or the parts of Percy Jackson that I'm using.**

 **I have no beta.**

 **ENJOY!**

 **CHECK ME OUT ON TUMBLR. THE LINK IS ON MY PROFILE. I FOLLOW BACK.**

* * *

Sherlock had resided in the waters of his home for years. Too many to count, but he did watch as the human - homo sapiens - advanced. From wooden seacraft to heavy, massive, crafts made of 'steel'. The humans added things to the Iron in order to make Steel, which was more durable.

There were no more pirates in his area. Not more sailors passing by either.

The nearest human settlement had started not too long ago. With homes growing from wood, to strange red bricks and white rock, with their buildings stretching into the blue sky.

Their transportation, 'automobiles' advanced as well. Sherlock was intrigued to learn how they were created and how they moved with aid of a horse.

Sherlock lived near a cove, surrounded by a beach. The humans called it Crystal Cove and though it was a good name, it was terribly inaccurate. The cove was half beach, half rocky cliff and the cliff was covered in hundreds of colorful gemstones, but none of them were crystal.

The outside of the cove, that faced the open waters of Poseidon's kingdom, was mostly blocked by large rock formations that shot up from the water, creating a blockade of sorts. Small fish, merfolk, and humans could fit through the spaces between them, but the strength of the current would be too much for the humans and they'd be pulled out and lost. The fish would be safe if they were far down enough. And merfolk, well, Sherlock had a lot of physical strength yes, but his most powerful asset was his tail.

It was long and covered in shining blue scales that matched the color of the water. A bright turquoise that sparkled in the sunlight, but glowed in the moonlight. Each scale was about the length of his smallest finger and they overlapped each other in triangular shapes.

He had two pelvic fins that flared out a little below his hips. They were long and while they looked flimsy due to being partially transparent, they were very durable.

His tail was extremely long and ended with a fan shaped caudal fin that was mutated. Unlike other merfolk whose caudal fins were shaped so they moved side to side in order to help them move, his fin was flat, resembling a human hand fan closely. It could not move from side to side, instead it moved up and down. While Sherlock had always been made a mockery of because of his mutated fin, he'd always been extremely faster that all the other merfolk, so he could cushion his ego on that fact.

Several inches above his caudal fin, were two anal fins, both on equal sides as the pelvic fins. They were long, reaching to his caudal fin easily and helped stabilize him so he didn't teeter around and lose course.

Sherlock was very different that most merfolk. Mermaids were usually the ones to have excessively, flowy fins. They had pelvic fins, merman didn't. But merman had adipose fins, which were found on the dip of their lower backs, mermaids did not have them. Sherlock both, which tended to keep the other merfolk besides his brother Mycroft, away. He had male and female body parts. He was… abnormal.

He didn't care. It wasn't like being 'normal' was amazing anyway.

Sherlock had swam for better residence the moment he reached his majority and he found his little cove that the humans sometimes ventured to in order to go for a swim. He would observe, they'd muck about, playing endless games and indulging in frivolity, and then they'd leave. Sometimes they'd forget their belongings and Sherlock would drag himself into the beach and then back to the water before they came back.

He had a whole collection of human objects in the small, underwater cave he resided in.

He'd like to understand them, but was satisfied enough with his treasures that he didn't seek the aid of any human. He knew of the stories. Fiction or not, he knew the humans would either be fascinated or terrified of him and both led to the same outcome. Experimentation, which he was not okay with. Either they'd want to see how his body functioned, or they'd want to learn of what he was and how properly to kill him. He was not a fool.

Sherlock resided within his little cove for many years, feasting on the fish that strayed too near, receiving random visits from Mycroft, and observing the humans to his heart's content.

But one day… something amazing entered his cove. It must have happened while he was sleeping, though he didn't understand how it made its way into the cove with the rocks blocking the only entrance via ocean. It was too big to fit inbetween the rocks, but Sherlock could not for the life of him, figure out how it appeared. But it was there.

It greatly resembled a horse, though the front legs thinned out into large fins. The body with similar with two pelvic fins in the proper space. Then it too thinned out into a very large, forked caudal fin that was flat like Sherlock's was! It was blue, not the same shade as Sherlock's tail was, but just as eye catching. More like cerulean. And there were small spots of rosy pink and bright violet here and there near the neck.

The crown of the head was adorned with pointed spines that trailed down the back of the neck and flattened against the creature's back until they were indistinguishable.

The eyes were the same color blue as the body. Just like Sherlock's were the same as his tail!

He swam closer to the creature, that eyed his approach warily.

He reached out carefully, longing to stroke the large neck of the beast.

It was cold! Much like he was.

"What are you?" Sherlock murmured to himself.

The head shifted and the creature pulled away from him. Its fins moved and then it was ascending toward the surface. Sherlock followed.

The creature breached the surface and headed for the sand. Sherlock followed suit, wondering what it was going to do.

And then, right before his eyes, the beautiful horse-fish morphed into a human!

* * *

 **A/N: First one is done.**

 **-My art for Sherlock is available on the AO3 version of this fic.**

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	2. Chapter 2

**A/N: Hello, people!**

 **I don't own Sherlock.**

 **I have no beta.**

 **ENJOY!**

 **CHECK ME OUT ON TUMBLR. THE LINK IS ON MY PROFILE. I FOLLOW BACK.**

* * *

Sherlock swam closer to the human, now realizing that it actually wasn't a human! Humans didn't have blue tinted skin. Some of them had various shades of brown, and some turned red after hours in the sun, but there was never any blue.

Also, this human shaped being was covered in little pink markings. Not like the decorations that many in his pod would get when accomplishing some major feat. Sherlock had many of his own all over his torso and face and arms. Once he reached particular ages or levels in intelligence, Mycroft would go about the process of embedding beautiful, carved shells into Sherlock's flesh. It was considered an honor. And there wasn't much pain thanks to Mycroft being quite good at the Healing Song. Almost all of Mycroft's flesh was covered in shells.

But no, the markings on the human like figure were like a part of the skin. Much like the 'tattoos' the humans mentioned every now and them. He'd seen them before. Artwork being permanently rendered into the flesh.

Sherlock swam nearer, curious.

The creature took shape of a human male, but that didn't mean it was male. Even with its impressive male like anatomy bared for Sherlock to see.

"What are you?" he reiterated.

The being's head cocked to the side, a look of confusion coming over its features.

It spoke! They were words he didn't understand mostly, but he did manage one of them. Lingua. That was what the humans called Latin. Humans had too many languages for one species.

Sherlock didn't not know Latin. He knew English, French, Spanish, Mandarin Chinese, and Russian. Hmm…

This would be rectified.

With a wide gesture, Sherlock waved the human like being closer. It walked on legs easily, obviously used to it. When close enough, Sherlock motioned for it to sit down. He was pretty sure it was male, but wouldn't know until they could understand each other.

When it sat, Sherlock pulled himself up beside it, sitting in the sand as the waves rushed back and forth up the beach. He crooked a finger and bumped foreheads with the creature when it leaned in.

He began to Sing lightly.

Merfolk had magic. Age usually depended on skill and how much magic. Sherlock was one of the old members of the pod. Not Mycroft's age obviously, but somewhere in the upper register. His yearmates all died before he did because they were idiots that got eaten by sharks. Fools they were for not listening.

Sherlock's magic was also very powerful, when he cared enough to try. Usually there wasn't a need for magic. He didn't eat humans like others did. They weren't fulfilling and usually tasted terrible from being unclean. He preferred fish. Angel Fish mostly.

Sherlock could heal, though not as good as Mycroft could. He could cause tempests, also not as good as Mycroft. But what he did have over his sibling, was his ability to share knowledge. With a little Song, Sherlock could transfer his knowledge of something to someone else. He'd only done it twice before and only to Mycroft as payment for a couple of favors.

But here and now, he wanted to know more about the creature, so he Sang his knowledge of English, imprinting it into the creature's very being.

Pulling away slightly, Sherlock asked, "What are you?"

Blue eyes sparkled instantly, "I am a male Hippocampus."

Sherlock became eager, curious to learn of this new creature. "And what are you named?"

"Jean."

Jean… a French name. English version… John.

"I will call you by your English name… John. I am _Mer'locke_ … but in English, which is what we are speaking, I am called Sherlock."

"Pleasure," John smiled.

Sherlock blinked, feeling himself flush a little. John was… attractive in his human form.

He shook himself a bit. "Do you have magic? How old are you? Are you full grown? Do you have any siblings? Do your kind have-"

John's hand slapped over his mouth. "One at a time. I have magic. I am an adult but am a bit smaller than the others my age. My sister is much larger than I am, as well as older."

John pulled his hand away. "My magic doesn't do much. I can simply shape shift into a humanoid form and heal. Others have greater ability. My sister can make water freeze and shoot it from her mouth. Our mother was able to manipulate water. My father was able to fell any creature so long as he focused his screams on it personally."

Sherlock was not deterred. "Are there many of you? Do you have tribes or pods or families? What do you eat? How do you spend your time? What sort of things have you seen?"

John smiled wider. "My family was rather small. I don't think there are many Hippocampi left in the world. The females have been rendered infertile for some reason and only the males can bear now, but most don't want to bear pups of their own, so we are slowly dying out. I eat fish. I like to practice my swimming and I avoid my sister because she becomes overbearing at times. She and her mate are loud. I've been to a lot of places and have seen a lot of things."

Sherlock's mind was working quickly, filling in gaps of knowledge. What really interested him was the fact that both males and females of their kind could bear children. Merfolk and humans couldn't do that.

John was interesting.

"Can you breathe underwater when not in your other form?" Sherlock asked.

John lifted his arm, revealing gills similar to the ones on Sherlock's neck. "Yes."

Sherlock grabbed his blue hand, "Come, John!"

He slipped into the water, pulling John with him.

Once they were fully submerged, Sherlock was able to fully relax now that he was back in his natural element. John's hand reached out, trailing sharp nail tipped fingers over Sherlock's pelvic fins.

Sherlock shivered. They were sensitive, he knew that. But it never felt like that when he touched them.

"How did you come to be in my cove? Did you walk in like the humans or swim in?"

John smiled, "I jumped off the cliff when I spotted some humans getting too close. I didn't want them to see me."

"Yes, I imagine it'd be difficult to explain your skin color."

"You're a merman, right?"

"Yes."

"I thought the fins went the other way," John observed, staring at Sherlock's tail.

"They do. I'm a special case," Sherlock huffed.

"That's amazing!" John smiled, staring at the mutated fin.

Sherlock flushed again. No one, not even Mycroft, had ever said that.

* * *

 **A/N: Another is done!**

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	3. Chapter 3

**A/N: Hello, people!**

 **I don't own Sherlock.**

 **I have no beta.**

 **ENJOY!**

 **CHECK ME OUT ON TUMBLR. THE LINK IS ON MY PROFILE. I FOLLOW BACK.**

* * *

Sherlock's days with John blended together. John was fun and liked things similar to what Sherlock liked. They would explore the depths of the cove and sometimes John would climb - yes, climb - the rocky cliff and pull the fanciful gemstones that grew there, for Sherlock.

Sherlock used shells to decorate his body. But Mycroft preferred gemstones. They glinted off the lights, making him even more striking in appearance. Mycroft always preferred the more ostentatious creations. That was why he even had a very large stones embedded in his chest, for the other merfolk to see.

Sherlock collected the gems for Mycroft in return for favors. And John had helped him, which earned him a favor.

John. John knew how to have fun. And he knew what the human appliances that Sherlock had stolen were called! Sherlock liked being able to talk to someone for once. Someone who didn't think he was a freak because his tail was mutated and he was both mermaid and merman.

John thought his body and its… differences to other merfolk, were amazing. And way he said the word, almost in reverence. It made Sherlock flush, because he'd never been treated so kindly before.

And then, nearly two weeks into their acquaintance, he came.

Sherlock had been lounging on the sand, the waves coming up to brush over his tail. John lay beside him, taking in the warmth of the sun.

Sherlock's sudden stiffening, made John's right eye open, the Hippocampus staring up at him questioningly.

"We are about to have a visitor," Sherlock warned, dragging himself toward the water until he was able to slip in enough to swim.

Sherlock was glaring in annoyance. He just had to come now, didn't he?

Mycroft swam in between the large rocks that blocked Sherlock's cove off from the ocean. His brother hadn't changed in the least. He was a bit larger than Sherlock but that was only due to age. His tail was more purple - probably mauve - than Sherlock's was. Though his own fins were colored the same as Sherlock's were. Mycroft's flesh was covered in gems, leaving only the skin of his hands and part of his face, visible. His eyes were a shade of blue darker then Sherlock's and slitted just the same.

"Hello, little brother."

"What do you want, Mycroft?"

"It's time for my biannual visit, brother mine, surely you haven't forgotten?"

Sherlock scoffed, "Of course not."

He did.

Not that it mattered.

"Well, you visited. You can leave."

Mycroft's eyes narrowed. "There is something you do not wish wish me to see."

Damn.

Mycroft moved to swim past him, but Sherlock deliberately moved in his way. John was his. He didn't want to share John's existence with anyone!

Mycroft gave him an unimpressed look. "Sherlock." His tone was full of warning.

Sherlock's words were cut off by the arrival of John. Blue skinned, obviously not a human, John. John was staring at Mycroft in wonder.

Mycroft was returning the look, but Sherlock saw it. Fascination. Intrigue. Arousal!

No!

Sherlock grabbed John's hand, tightening his fingers around it. "Mycroft, this is John. John, my annoying brother, _Mer'crofte_."

John smiled charmingly at Mycroft, making Sherlock bristle. Mycroft did nothing to earn that smile.

Mycroft took his other hand, turning it over and placing a kiss on the pulsepoint. Sherlock was ready to spit fire.

"A pleasure. May I ask what species you are from?"

"I'm a Hippocampus."

The shine in Mycroft's eyes told Sherlock that he knew exactly what John was.

"Interesting. And his long have you known my little brother?"

"A few weeks."

"And you stayed."

"Yes. He's extraordinary."

Sherlock flushed, probably for the millionth time since knowing John. John was always complimenting him. It was… nice.

"Indeed," murmured Mycroft, looking back and forth between them. "And you have no desire to see the rest of the ocean, John?"

"Not unless Sherlock is with me, no."

Sherlock was warm again. No one ever said anything like that either.

"Perhaps, if you do not wish to venture out yet, you'd like to meet a mermaid? She wished to meet Sherlock and I feel that you'd all get along swimmingly."

Sherlock knew what this meant. A mermaid that Mycroft wanted him to meet meant that she was new to the pod. And Mycroft was going to try to set them up because she hadn't met Sherlock yet and couldn't form an opinion. He was also hoping that Sherlock would take an interest in the mermaid and that would then leave John for Mycroft's perusal.

Not happening.

John agreed and Mycroft swam away with a promise to return shortly.

Sherlock huffed.

"Sherlock?" John said, giving him an inquisitive look.

"Yes?"

"Why does your brother look like stained glass?"

"Pardon?"

Sherlock never heard that term before.

"Um… humans can color glass, which is made from heating sand. They make it look similar to gemstones and such. Your brother looks like a fancy window of stained glass I saw once, in a church that overlooked the ocean."

Sherlock sighed. "There are many reasons, John. First is that Mycroft is one of the oldest in the pod and of the oldest, he is strongest, making him the leader. He has had more time.

You see the markings on my flesh?"

John nodded, reaching out to run a finger over the shells embedded into Sherlock's left shoulder.

"They are rights we merfolk earn in our lives. Reaching majority is one of them. Defeating a large enemy is another. A successful first hunt. Discovering a new species unknown to the pod. First kill. Things of these natures, earn you the right to markings.

The marks are usually made by gems, shells, stones, or even branding. I prefer to use shells that accentuate my tail. Mycroft however, is very flashy and likes attention. No matter the time of day, he is always striking above the water."

Sherlock sighed, feeling a little resentment toward his brother.

"The large pieces you saw on his chest and arms show that he has faced large adversaries before, whether he wanted to or not. Mycroft is what a respectable leader should be apparently. Also, he has the most markings out of the whole pod."

Sherlock's eyes rolled. "It's ridiculous."

"I wouldn't say that. It's just... his tail doesn't match."

Sherlock stifled a snort.

A moment later, Mycroft returned with a mermaid in tow. She was smaller than them, with a dainty torso that was covered in small black stones that stood out from her pale flesh. Her hair was just as black and was pulled back in a loose bun. One tendril of hair curled over her forehead. Her eyes were a grey/blue that reminded Sherlock of stormy waters. Her tail was also grey with large black pelvic fins that matched her caudal fin and anal fins.

She was smirking at him.

"Sherlock, John, meet _Mer'ene_."

* * *

 **A/N: Another one is done.**

 **-CHECK THIS STORY OUT ON AO3 IF YOU WANT TO SEE THE ART I MADE!**

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	4. Chapter 4

**A/N: Hello, people!**

 **I don't own Sherlock.**

 **I have no beta.**

 **ENJOY!**

 **CHECK ME OUT ON TUMBLR. HELLY-WATERMELONSMELLINFELLON. I FOLLOW BACK.**

* * *

John was not pleased.

He'd been sunbathing with Sherlock, just enjoying the merman's company, when their solitude was interrupted. It was nice to meet Sherlock's brother and all and to learn some more about merfolk and their culture, but he did not want to meet anyone else.

But his mother had taught him proper manners and he wasn't about to be rude, so he agreed,

And she was horrible!

Actually she was rather beautiful but John did not like the look she was sending his Sherlock!

Mycroft on the other hand was giving John a very familiar look. One that he was not interested in reciprocating any time soon.

Thankfully, Sherlock did not seem to be interested in the mermaid.

"It's lovely to meet you," she smiled, her teeth abnormally white, lips outlined in black.

"Hm."

Sherlock wasn't exactly one for niceties and his brother didn't appreciate his prompt disinterest.

"This is Sherlock's… friend, John."

He took too long to say the word 'friend'. Why? Sherlock was a perfectly agreeable person. There was nothing wrong with him!

"Irene," Sherlock said suddenly, dropping the pronunciation of merfolk names and translating it immediately. "Abnormal fixation on your appearance shows vanity encouraged by low self esteem. Brazen use of black stones show a need to be in control. Dominance issues. Would never have a merman because they tend to be domineering and prefers mermaids. Your time here is wasted."

John and Mycroft reacted with amazement, but then branched off. Whereas John though it was spectacular and wanted him to do it again, Mycroft's head fell into his hands.

"I apologize for him, he never learned to hold his tongue not matter how hard I tried."

Irene was smirking however. Her stormy eyes raked over Sherlock's long frame, stopping on his pelvic fins twice. John rumbled in protest, barely keeping the sound to himself.

"It's alright. I actually find myself intrigued. You consider yourself a merman even though you possess both male and female fin types?"

"Obviously," Sherlock sneered, glancing down at his chest. "I may have both fins but I still have a Pachynsis which only males have."

John sent him a look that conveyed his confusion over what he just said. Sherlock, ignoring both Mycroft and Irene's shock at his blunt words, simply said, "The merman's sexual organ. It resides in the same place where yours does," he said, motioning to John's impressive human shaped manhood.

"Ours are attached to a layer of our tails that sort of peels off when mating. Imagine this area," Sherlock said, gesturing to his hips where his flesh bled into his tail in sharp, jagged lines, "coming down a bit, and there it resides until finished. I have one, so that makes me male. Just because I look better than most mermaids, and can even pull off being one better, it does not mean I _am_ a mermaid."

Mycroft looked mortified and Irene seemed interested still.

John, though jealous at how she was reacting, couldn't help but be interested. He liked it when Sherlock explained his kind. Hippocampi weren't known for sharing waters with merfolk, so he didn't know much and he clung to every word Sherlock gave him.

"And I might as well just say this now in case I wasn't being clear enough with my lack of attention. Mermaids do not interest me. And John is mine. You can leave now."

Sherlock turned around and grabbed John's hand.

"Let's go. I want you to tell me about sermons and why humans find it necessary to pray to a God who isn't part of the Olympians."

John followed immediately, making sure to send a haughty smirk Irene's way. Sherlock wasn't interested. Get lost.

Sherlock took them to his cave and not saying a word until they were safely ensconced within. "You do realize that my brother does not give up and both will no doubt be coming around often?"

John frowned. "Why? You said that you weren't interested. Shouldn't that be enough?"

Sherlock scoffed, his perfectly lips turning down. "No. Mycroft is stubborn and wants me settled down to contribute to the pod's life by adding hatchlings. He's pushed all the mermaids on me and none of them stuck around. This one is odd however, she'll be a tricky one. Though it isn't really me she's interested in. It's more my appearance."

Oh.

"Mycroft also seems to be interested in you simply because you like me and no one else does. Mycroft will attempt to charm you. Do no fall for his charisma nor his Song."

"What about his Song?"

Sherlock sighed. "The Song, John! The Song is where our magic comes from. We can heal, cause great tempests, kill if skilled enough, and so many other things. He could seduce you easily. It's how he hunts for the pod. Mycroft's Song is particularly enchanting and it draws fish and humans in quickly."

"Okay, I'll be careful," John reassured with a smile. A worried Sherlock wasn't a happy Sherlock. He preferred it when Sherlock was content and explaining something about some kind of fish or another. He seemed so carefree that way. By being himself.

"You do that. I won't leave you alone for a moment."

He liked the sound of that.

They both sat on the bottom of the small underwater cave, just enjoying each other's company, when Sherlock - out of the blue - asks, "How do Hippocampi mate?"

John's blue cheeks became purple as he flushed.

"Well, since our normal forms are slippery thanks to a gel we secrete to keep us from getting stuck between spaces, it is difficult to mount. We have our human forms for mating. The reproductive organ is inserted within either orifice and copulation occurs."

Sherlock was nodding, completely oblivious to the fact that John was flushed to the tips of his ears and was uncomfortable.

The blue eyes merman turned to him and said, "Have you ever mated?"

John was pretty sure that in that moment, something inside of him broke apart, revealing this extremely hot and bothered being that wanted to demonstrate all it had learned.

"Yes."

Sherlock's eyes sparkled. "What was it like?"

* * *

 **A/N: Another is done.**

 **How was it? Let me know.**

 **Check out my other fics. I updated a bunch today!**

 **See ya! :D**

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